1. Field of Invention
This invention relates to improvements in methods and apparatuses for dynamic information storage and retrieval, and more particularly to improvements in dynamic information storage systems of the type having associated mass data storage devices, such as DVDs, CD-ROMs, or like devices, and still more particularly to improvements in methods for managing, allocating, or controlling a cache memory in such dynamic information storage and retrieval systems depending upon the specifications of mass data storage devices associated therewith, and systems for using same.
2. Relevant Background
As used herein, the term “dynamic information storage system” includes digital systems that have one or more mass data storage devices to which digital data may be selectively written and read back. Some dynamic information storage systems, for example, may include one or more digital video disk (DVD) devices alone, or in combination with one or more compact disk read-only memory (CD-ROM) devices. The data storage devices may be interfaced to a system bus, a typical bus that is currently popular in use being, for example, the ATAPI bus, although other buses can be used.
Mass data storage devices include tape drives, RAM drives, as well as hard disk drives that have one or more spinning magnetic disks or platters onto which data is recorded for storage and subsequent retrieval. Hard disk drives may be used in many applications, including personal computers, set top boxes, video and television applications, audio applications, or some mix thereof. Applications for hard disk drives are still being developed, and are expected to further increase in the future. Mass data storage devices may also include optical disks in which the optical properties of a spinning disk are locally varied to provide a reflectivity gradient that can be written and detected by laser transducer heads, or the like. Optical disks may be used, for example, to contain data, video signals, music, or other information.
In dynamic information storage systems, typically a host device or system may be required to interface to the system, yet, as mentioned, a single dynamic information storage system may include either a DVD type, CD-ROM type, or both types of mass data storage devices. Such devices are now being provided, for example, in systems in which both audio and video data can be written to the respective mass data storage devices associated with the system. This can create a problem in that relatively long times are required in order to fully record data to DVD systems, especially in comparison to the relatively shorter time that is required to write audio data to a CD-ROM mass data storage device. Because the wait times of different types of mass data storage devices may differ, the efficiency of the system may not be optimal for a particular host.
Typically, in the construction of dynamic information storage systems, the communication between a host and the associated mass data drive(s) should be taken into consideration. If, for example, a DVD drive is included, the system would typically have a long busy time during communication, because DVD drives have a slow response. This factor restricts the freedom of the structure of the host. For example, in order to accommodate the long busy time, the host needs a large memory as a communication buffer. This makes the system larger and more complex than otherwise would be required if the busy time were not so long.
In the design of DVD drives, and particularly in the combination of a DVD drive with a host device, typically trade-offs need to be made. For example, some DVD drives have different busy and overhead times, but, nevertheless have the same DVD writing speed.
In some applications, a small overhead time may be better in a system in which the data transfer frequently changes direction, for example, in a read/write operation. On the other hand, in other installations, a small busy time may be better in a system in which the host performs a number of write operations to the DVD device in frequent succession. As will be seen in the detailed description below, the overhead and busy times depend upon the size of the cache.
In the past, however, the size of the cache could not be changed in the design the system. Therefore, depending upon the particular application, it has been important to select the proper drive to meet the particular needs of the application. For example, a drive having a small overhead time may be selected in those applications which have frequent changes in the data direction. Moreover, once the drive is selected to meet the particular application needs, the host device needs to be selected to adapt to the particular drive that is selected.
This difficulty is further compounded when a system is designed in which several applications may be combined into a single device, and, in particular, in cases in which some applications require a short overhead and other applications require a short busy time. In the past, the design of a host in such cases was a trade-off considering the unchangeable characteristics of the drives.
What is needed, therefore, is a method and system that provides efficient communication between a host and its associated data storage systems, regardless of the construction of the dynamic information storage systems with regard to the types of mass data storage devices associated therewith.